Tests and Procedures

Kidney Stone (Urine)

Does this test have other names?

What is this test?

This test checks your urine for chemicals that might cause your body to form kidney stones. The test also looks for blood in your urine, which can be a symptom of kidney stones.

Kidney stones are hard masses of minerals and salts that can form in your kidneys. They can be as small as a grain of sand or more than an inch in diameter. Usually theses stones or crystals pass through your body when you urinate. But sometimes they can get stuck in your urinary tract and cause a lot of pain.

Why do I need this test?

You may need this test if your doctor suspects that you have kidney stones. Symptoms of kidney stones include:

Pain in your lower belly or side

Nausea and vomiting

Sudden, strong urge to urinate

Pain when urinating

Blood in your urine

You may also have this test if you had a kidney stone or you are being treated for kidney stones. If you have had a kidney stone or any treatments for a kidney stone, you should wait one to two months, or until you have completely recovered, before having this test.

You will need to repeat the test at least twice so your doctor can compare the results.

What other tests might I have along with this test?

Your doctor may also order imaging tests including a CT scan and a special type of X-ray that uses a dye to look for kidney stones.

Your doctor is likely to order blood tests, too, to look for calcium, uric acid, oxalate, and citrate, which are some of the chemicals that are most likely to cause your body to form kidney stones.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Results are given in milligrams per day (mg/day). The results will show whether your urine has high or low levels of the chemicals that are most likely to cause stones to form. These chemicals are calcium, uric acid, oxalate, and citrate.

Normal levels for adults vary depending on your gender and the chemical:

Calcium: less than 250 mg/day in women or less than 300 mg/day in men

Uric acid: less than 750 mg/day in women or less than 800 mg/day in men

Oxalate: less than 45 mg/day for women and men

Citrate: greater than or equal to 320 mg/day for women and men

If your levels are not normal, it may mean that you have a kidney stone or stones.

Abnormal levels may also mean that you have another kidney disorder, such as a urinary tract infection.

How is this test done?

This test requires a 24-hour urine sample. For this sample, you must collect all of your urine for 24 hours. Empty your bladder completely first in the morning without collecting it and note the time. Then collect your urine every time you go to the bathroom over the next 24 hours.

Does this test pose any risks?

This test does not pose any known risks.

What might affect my test results?

Having this test too soon after treatment for a previous kidney stone can affect your results. You should wait several months after treatment before having this test.